"All my brothers, come to jihad," says another fighter, who is also identified as British. "Feel the honor we are feeling, feel the happiness that we are feeling."

The third fighter to address the camera is identified as Australian.

It's not clear where exactly the video was taped, though the fighters make reference to "the land of Sham," a term used to describe Syria and portions of neighboring countries.

"We have participated in battles in Sham, and we will go to Iraq and fight there in a few days," says the first fighter.

The video was uploaded Thursday to the English-language Twitter feed of a group called Al Hayet Media Center. According to Flashpoint Global Partners, a group that tracks terrorism, Al Hayet Media Center is not formally associated with ISIS, though it is one of a few media organizations that ISIS promotes on its own social media accounts.

"It preaches specifically to foreign fighters, especially to those in the West," Laith Alkhouri, a senior analyst with Flashpoint Global Partners, said of Al Hayet Media Center.

Alkhouri said that Al Hayet Media Center maintains Twitter accounts in a number of languages, including English, French and German.

ISIS is among a number of jihadist groups operating inside Syria and Iraq. The exact number of foreign fighters associated with ISIS is unknown, but two recent studies put the number of foreign fighters in Syria above 10,000.

A study released in December by the International Centre for the Study of Radicalisation, a group associated with King's College London, estimated that there are up to 11,000 foreign fighters in Syria. Of that number, the report estimated, up to 2,000 fighters come from Western European countries.

Another study, released this month by the Soufan Group, a private consulting company with offices in New York, estimated there are more than 12,000 foreign fighters in Syria, with about 3,000 coming from Western European countries.

Citing the FBI, the Soufan Group said dozens of Americans, possibly 70 or more, have traveled to Syria to fight.

Terrorism analysts say that the video also points to a sophisticated media strategy.

"A release in English is going to get them more play in our media," said Brian Fishman, a fellow at the New America Foundation.

"They study us. They study us closely," Fishman said. "They know that when there is a release in English we not only talk about it more, we reflect on what it means."

First published June 20 2014, 9:09 PM

James Novogrod

James Novogrod is an NBC News producer. Previously, he worked as a political reporter and embedded with the Michele Bachmann presidential campaign. After Bachmann dropped out of the race, he covered state primaries, the "veepstakes," the Republican and Democratic National Conventions, and the presidential election.

Additionally, he spent May through mid-July 2012 in the Orlando area covering the Trayvon Martin story.